The musical drum is believed to be the earliest instrument developed by man. Drum evolution has continued from the earliest times and continues in the present. Today, modern musical drums are often made by wrapping numerous plies, usually thin sheets of wood or other material, into a laminated annular ring with an annulus of varying length depending on the properties that one desires for the particular drum construction. The annulus is called a drum shell.
Over the end or ends of the annulus a drum head, made of plastic, hide or other flexible material is stretched to provide a resonating surface which can be struck to create the sound made by the drum.
Often only one end of the drum shell is covered with a drum head, but when both ends of the annulus are covered, the end that is made to be struck with the hand or some other beater such as a drumstick or a mallet is called the batter head and the opposite head is called the resonance head.
To get the maximum range of effectiveness from a drum it is desirable to imbue a drumhead with the potential for as many vibrational modes as possible. The more perfectly circular the drum is; the easier it will be to excite a range of vibrational modes in the drum head. For a circular drum head these modes can be defined mathematically by Bessel functions, and they correspond to patterns of nodes and antinodes on the vibrating surface of the drumhead. Each mode further corresponds to its own set of vibrational displacements of the drumhead with modes that exhibit more complex arrangements of nodes and antinodes producing higher frequency sounds from the drum.
The bearing edge of the drum heads, that is the edge over which the drum head material is stretched, places boundary conditions on the vibrations of the heads, and any permitted deformation at the edge can lead to different drum sounds. Various edge angles are commonly machined into bearing edges to control edge deformations as the vibrations approach the edge of the drum head. Drums can be tuned by varying the tightness of the stretch to control these edge deformations, and the overall sound of particular kinds of drums are often dependent on how much edge deformation is allowed.
Although many drum enthusiasts emphasize the importance of the drum heads to the tuning and sound made by the drum, the nature of the drum shell is also of fundamental importance to the overall sound made by any particular drum.
For example, when a thin laminated shell is used, such as an eight ply shell, the resulting drum usually has a lower pitch and has a darker tone. On the other hand thick shells tend to have a brighter tone with higher pitch and tend to project well in a loud musical environment.
Other shell designs are common such as using a thin shell as discussed above but adding reinforcing hoops at the top and/or bottom of the shell. This leads to a more general purpose kind of drum providing a range of tones between the high and low tones discussed above.
Laminated drum shells employ various adhesives to hold the laminates together. These adhesives usually have poor acoustical properties and tend to act as sound deadeners in the shells leading to poorer resonance than would otherwise be provided by the shells.
In contrast to laminated shell drums, wood stave drums are made by methods similar to constructing a wooden barrel. To make these drums individual pieces of wood are cut and shaped to fit together to form a shell. The pieces can be joined together by various methods such as butting, splining, or even tongue and groove and are often held together using an adhesive. As with a wooden barrel, the resulting structure is strong and unyielding largely due to the approximately circular geometry of the structure. Once joined, the shell can be machined to a circular shape both inside and outside the shell. Often wood stave shells are simply turned on a lathe to smooth their surfaces and make them round.
The tonal response of such a drum is enhanced by the solid wood shell. Wood stave drums exhibit excellent musical response as well. Much of this is attributable to the usually vertical grain pieces of wood from which the staves are cut with the bearing edges of the drum at the end of the grain extending from stave to stave substantially perpendicular to the grain so that the plane of the drum head is substantially perpendicular to the grain of the staves. These vertical grain structures conduct the drum head vibrations through the shell very effectively.
Further, when used, adhesive bonding between the staves does not attenuate shell vibrations the way a laminar structure does. In the case of a laminar shell the drum head rests on the bearing edge with the plane of the drum head nearly always parallel to the grain of at least some of the laminates. This configuration is necessary because the strength of the laminated plies of the drum shell need to be parallel to the circumference of the laminated shell to strengthen the shell so that the plies will not break.
In addition the actual quantity of acoustically deadening adhesive used in a wood stave drum is much less than that used in a laminate drum shell. Some estimates have placed the adhesive used to construct a wood stave shell at about 0.0001 of that used for a 9 ply glue laminate shell.
All of this leads to wood stave drums with consistently true, melodic tones high in quality when compared to laminated shell drums.
The ability of head vibration to be transferred to the shell can have a substantial effect on the sound of a drum. Similarly, the design of a shell can significantly change the sound of a drum. Most drums are made of wood, and shell resonance is at least partially dependent on the kind of wood used.
Sound vibrations tend to be carried through harder and denser woods more efficiently than they are through softer, less dense woods giving harder woods higher tones with more projection and softer woods lower tones with less projection. Nevertheless, each kind of shell wood has its own properties with regard to frequency distribution giving each wood used a different sound.
In modern drum performances the look of the performers' instruments can be as important as their sound. Because of this, recent drum constructions have employed all kinds of decoration from bright colors to internal lighting inside drum shells sometimes responsive to individual beater strikes.
Though not commonly employed, drum vibration can be changed by inserting acoustic modifiers into the shells. Modification has been accomplished by various methods from fabric pads attached to the shells to modifying drum shells with breather holes.
Hence, drums are now at the evolutionary point where sounds as well as looks are important and new methods of accomplishing new designs incorporating both are needed.